The present invention relates to the oxidation of cyclohexane for the production of cyclohexanol and cyclohexanone and most particularly to the use of liquid oxidation reactors using pure oxygen or oxygen enriched air and operating at temperatures which are somewhat lower or with reaction contact times which are shorter than conventionally used in cyclohexane oxidizers.
Most of the worldwide production of caprolactam and adipic acid, which are used in the manufacture of synthetics such as nylon, is based on the air oxidation of cyclohexane. The air oxidation of cyclohexane produces cyclohexanol and cyclohexanone and a variety of potential cyclohexanol and cyclohexanone precursors such as hydroperoxides which are then thermally and/or catalytically decomposed to produce additional cyclohexanol and cyclohexanone. The cyclohexanol and cyclohexanone are then used to produce either the caprolactam or adipic acid. The prior art processes for oxidizing cyclohexane employ air and operate at temperatures in the range of 130 to 180.degree. C. in bubble columns or autoclaves. At the lower temperatures, 130 to 160.degree. C., the reaction rates tend to be lower although the selectivity for the desired precursors is higher. At higher temperatures, the reaction rates increase but the selectivity is lower and more lower valued byproducts are produced.
The reaction rate and selectivity would be increased by raising the partial pressure of the O.sub.2 above 21% but that cannot be done using conventional oxidizing systems because of safety problems. If the oxygen concentration is increased, to any significant degree, the oxygen level in the gas phase above the liquid increases and can readily reach a flammability limit which is usually above about 1% oxygen.